article nature genetics volume 20 december 1998 337 SURF1, encoding a factor involved in the biogenesis of cytochrome c oxidase, is mutated in Leigh syndrome Zhiqing Zhu 1* , Jianbo Yao 1* , Timothy Johns 1 , Katherine Fu 1 , Isabelle De Bie 1 , Carol Macmillan 1 , Andrew P. Cuthbert 3 , Robert F. Newbold 3 , Jia-chi Wang 4 , Mario Chevrette 4 , Garry K. Brown 5 , Ruth M. Brown 5 & Eric A. Shoubridge 1,2 *These authors contributed equally to this work. Leigh Syndrome (LS) is a severe neurological disorder characterized by bilaterally symmetrical necrotic lesions in subcortical brain regions that is commonly associated with systemic cytochrome c oxidase (COX) deficiency. COX deficiency is an autosomal recessive trait and most patients belong to a single genetic complementation group. DNA sequence analysis of the genes encoding the structural subunits of the COX complex has failed to identify a pathogenic mutation. Using microcell-mediated chromosome transfer, we mapped the gene defect in this disorder to chromosome 9q34 by complementation of the respiratory chain deficiency in patient fibroblasts. Analysis of a candidate gene (SURF1) of unknown function revealed several mutations, all of which predict a truncated protein. These data suggest a role for SURF1 in the biogenesis of the COX complex and define a new class of gene defects causing human neurodegenerative disease. 1 Montreal Neurological Institute, 3801 University Street, Montreal, Quebec, Canada H3A 2B4. 2 Department of Human Genetics, 1205 avenue Dr. Penfield, McGill University, Montreal, Quebec, Canada H3A 1B1. 3 Department of Biology and Biochemistry, Brunel University, Uxbridge, UK. 4 Montreal General Hospital Research Institute, Department of Surgery, Urology Division, McGill University, Montreal, Canada. 5 Genetics Unit, Department of Biochemistry, Oxford University, South Parks Road, Oxford, U.K. Correspondence should be addressed to E.A.S. (e-mail: eric@ericpc.mni.mcgill.ca). Introduction LS is a subacute neurodegenerative condition characterized by bilaterally symmetrical necrotic lesions in the brainstem, basal ganglia, thalamus and spinal cord 1–4 . Microscopically, these lesions are associated with vascular proliferation, gliosis, neu- ronal loss, demyelination and cystic cavitation. LS onset usually occurs in infancy, but adult cases have been reported 5,6 . LS is a genetically heterogeneous disease caused by defects in enzymes involved in aerobic energy metabolism. These include the X- linked E1α subunit of pyruvate dehydrogenase 7,8 , the mtDNA- encoded ATP6 subunit of ATP synthase 8–10 , respiratory chain complex I (refs 8,11,12) and COX (refs 3,8,11,13). It has also been found in association with point mutations in mitochon- drial tRNA genes 6,8,14,15 and a mutation in the F p subunit of succinate dehydrogenase 16 . Systemic COX deficiency presenting as LS is inherited as an autosomal recessive trait and is one of the most common causes of LS; however, the underlying molecular defect remains unknown. COX activity in these patients is reduced in all tis- sues of the body, often to very low residual levels, with little or no tissue specificity in the severity of the defect 17,18 . A bio- chemically distinct form of LS with COX deficiency exists in the French-Canadian population in which the brain and liver are severely affected and fibroblasts and skeletal muscle are rel- atively spared 19 . Somatic cell genetic studies have demon- strated that the majority of patients with the classic form of COX-deficient LS belong to a single genetic complementation group 20,21 . DNA sequence analysis of cDNA for all 13 struc- tural subunits of the COX complex, in both the classical and French-Canadian forms of the disease, have not revealed any pathogenic mutations 22,23 . This is consistent with earlier bio- chemical and molecular genetic studies that suggested a failure to assemble an active enzyme complex as the basis of the lack of enzyme activity 17,18,24 . The assembly of COX requires the expression of a much larger number of genes than those encoding the structural subunits of the complex. More than 30 different genetic complementation groups for COX assembly have been identified in yeast 25,26 . Many of these, such as factors that modulate translational efficiency 27,28 by binding to the 5´ or 3´ UTR of mtDNA-encoded COX subunits, probably do not have mammalian homologues, as mammalian mitochondrial mRNAs do not have UTRs. Although human COX assembly genes have been identified that could be considered potential candidate genes for LS (refs 29,30), the number and identity of the genes involved in COX biogenesis in mammals remains largely unknown. Identifying the genetic defect in COX-deficient LS by sequenc- ing candidate genes as they are identified is, therefore, an uncer- tain prospect. Likewise, the small family size in most cases precludes gene mapping by conventional linkage analysis. To cir- cumvent these problems, we have attempted to map and identify the defective gene by functional complementation of the enzyme defect in patient cells, using microcell-mediated chromosome transfer 31 . We show here that transfer of a normal human chro- © 1998 Nature America Inc. • http://genetics.nature.com © 1998 Nature America Inc. • http://genetics.nature.com